Realization of band gap above 5.0 eV in metastable cubic-phase MgxZn1−xO alloy films

We report on the realization of wide band gap (5–6 eV), single-phase, metastable, and epitaxial ${\mathrm{Mg}}_x{\mathrm{Zn}}_{\text{1−x}}\mathrm{O}$ thin-film alloys grown on sapphire by pulsed laser deposition. We found that the composition, structure, and band gaps of the ${\mathrm{Mg}}_x{\mathrm{Zn}}_{\text{1−x}}\mathrm{O}$ thin-film alloys depend critically on the growth temperature. The structural transition from hexagonal to cubic phase has been observed for (Mg content greater than 50 at. %) $\text{(1⩾x⩾0.5)}$ which can be achieved by growing the film alloys in the temperature range of 750 °C to room temperature. Interestingly, the increase of Mg content in the film has been found to be beneficial for the epitaxial growth at relatively low growth temperature in spite of a large lattice mismatch between sapphire and cubic MgZnO alloys.